In this paper, we propose an early block type decision method to reduce the complexity of rate-distortion (R-D) cost calculation in intra prediction. We established a method to decide early the best block size among luma 4x4, 8x8 and 16x16 for R-D optimized mode decision. The proposed method used R-D cost of a subblock ( 8x16 block ) instead of that of macroblock (MB) with the proposed encoding order for the intra prediction of 4x4 and 8x8 block. The R-D cost of a subblock is composed of luma components only. Chroma components have small potion of all R-D cost because they are used subsampling (4:2:0) and has relatively small variance between chroma pixels. Our method provides the reduction of computational complexity with average 0.04dB PSNR degradation and rate increase of less than 1% compared with the full search method.